The invention relates generally to railway car truck friction damping arrangements, and more particularly to a railway car truck friction shoe.
The present invention is directed to a friction wedge or shoe for a railroad car truck and in particular to a friction shoe including a body having a sloped face and a vertical face. The friction shoe dissipates energy throughout the range of suspension travel and compensates for wear over years of use.
Railroad car trucks of a design known as a three piece railway car truck include a pair of spaced apart side frames and a bolster that extends transversely between the side frames. The bolster is resiliently supported at each end on a respective side frame by a plurality of suspension springs. Wedge shaped friction shoes are used in such railroad car trucks to dampen movement of the bolster with respect to the side frame of the railroad car truck. Friction shoes are usually generally triangular wedge shaped such that two laterally spaced sloped faces are each in contact with one of two laterally spaced sloped faces of the bolster. The friction shoe is also comprised of a vertical face that is in contact with a corresponding wear plate mounted on a vertical face of a side frame column. Accordingly, the friction shoe acts as a motion damping wedge between the bolster and the wear plate on a vertical column of the side frame.
The wear plate on the vertical column of the side frame is usually comprised of steel. The friction shoe is wedged into engagement between the sloped faces of the bolster and the vertical column of the side frame by a suspension spring. Resistance to sliding movement of the friction shoe with respect to the side frame, which in turn provides dampening of vertical bolster movement, is provided by the frictional forces generated between the friction shoe vertical face and a wear plate on the side frame vertical column. The wedge shape of the friction shoe and the springs that force the friction shoe upward between the vertical column of the side frame and the sloped faces of the bolster provides automatic compensation for wear in the system. As the friction shoe, bolster, and side frame column wear with use over time the spring forces the friction shoe into the increasingly available space. As a result, the friction shoe automatically compensates for wear and rises relative to the bolster as the system wears.
In normal operation the friction shoes also move laterally in the friction shoe pockets in the bolster and wear against the side wall of the pocket. The foundry process used to make the hollow friction shoe generally utilizes holes in the triangular side walls to support the part of the mold that creates the hollow inside of the friction shoe. As the friction shoe wears against the side walls of the bolster friction shoe pocket the holes leave “islands” of unworn material which can interfere with or prevent the friction shoe from rising to take up wear in the bolster slope surfaces and side frame column surfaces.
It is an object of the present invention to provide an improved railway car truck friction shoe wherein the friction shoe and bolster can have a longer wear life and the friction shoe will not get stuck in the bolster.